Widely known in the art is a process for manufacturing twisted wire articles with variable direction of twist, comprising the steps of twisting and untwisting wires in the gap between a feed mechanism and a twisting head and of forming a finished article in the zone between the twisting head and a take-up mechanism as a result of continuous movement of wires along with the production process.
A disadvantage of said prior art process consists in that the twisting and untwisting of wires in the gap between the feed mechanism and the twisting head is effected with a pitch increasing with the distance from the twisting head. This results in a reduced number of lays and restricted length of article portions twisted in a single direction which, in turn, leads to frequent reversal of the twisting process and, consequently, lower efficiency.
In the machine for accomplishing said prior art process, the alternate twisting of articles in the right- and left-hand directions is effected as a result of continuous movement of three wires along with the production process and reverse rotation of the twisting head located in the gap between the feed and take-up mechanisms, provided the distance between the feed mechanism and twisting head is considerably greater than that between the twisting head and jaws provided between the twisting head and take-up mechanism.
The period of reversing of the twisting head decreases with an increase of the speed of its rotation, however, the minimum value of the period of reversing is limited and depends on the kinematics of actuating mechanisms, which means that the speed of rotation of the twisting head is likewise limited, this serving the main obstacle to increasing the output of twisted wire articles with variable direction of twist.
Japanese Pat. No. 20672/68 teaches a process for manufacturing twisted wire articles with variable direction of twist, providing for a continuous feed of wires to the zones of preliminary and final twisting. While so doing, in the zone of preliminary twisting the wires are twisted in one of the preset directions while in the final twisting zone the wires are twisted in the opposite direction. After that, the untwisting of pre-twisted wires takes place in the preliminary twisting zone simultaneously with the twisting of wires in the opposite direction in the final twisting zone.
In addition, for increasing the efficiency of the machines designed to accomplish said process, provision is made of means for additional twisting of the article in the final twisting zone, fashioned as a rotary support mounted between the twisting jaws and pull-out mechanism.
However, the additional twisting of the article results in a non-uniform pitch of twist in a finished article and, consequently, affects the quality and performance characteristics of the finished article.
U.S.S.R. Inventor's Certificate No. 501,127 discloses a machine for manufacturing twisted wire articles with variable direction of twist. Said machine comprises an unwinding unit, a twisting mechanism, a pull-out mechanism, a take-up mechanism, twisting jaws and a twisting head.
The unwinding unit of the machine is located at a distance of 7 to 10 m from the twisting mechanism in order to ensure the pre-twisting of wires in this zone.
The maximum output of said machine is attained at the minimum permissible period of reversing of the twisting head. While so doing, the number of revolutions of the twisting head during the period of its reversing, i.e., the twisting head speed of rotation upon which the machine output ultimately depends, is equal to the number of lays of the article wires in the zone of preliminary twisting. Increasing the length of the preliminary twisting zone for increasing the number of lays therein with a view to raising the machine output is only practical up to a certain point because the dependence between the two parameters in non-linear and such that, while the distance from the twisting head increases, the increment of the number of lays of preliminary twisting corresponding to one and the same increment of the zone length gets smaller.
This sets limits on the machine output.
Besides, the length of the article portions twisted in a single direction depends directly upon the number of lays of preliminary twisting while in a number of cases when twisted articles with variable direction of twist are used, for example, sawing ropes, the length of said portions should be varied over a wide length, this being possible in the prior art machine up to a certain point only.
In view of growing demand for twisted wire articles with variable direction of twist, in particular, for ropes designed for abrasion sawing of natural stone, prior art processes and machines fail to satisfy the ever growing need for such articles. Therefore, the development of more advanced processes aimed at increasing the efficiency of manufacturing twisted wire articles with variable direction of twist is a matter of urgent necessity.